INGRID: A near-infrared camera for the William Herschel Telescope

Rapid developments in near-infrared (NIR) arrays and adaptive optics systems have driven the development of wide-field and high-spatial-resolution, high-optical-quality NIR imagers and spectrographs, providing an unparalleled boost to NIR observations. Based around a 1024 × 1024 pixel2 Hawaii-1 array, the Isaac Newton Group Red Imaging Device (INGRID) imager provides a field of view >16 arcmin2 (at the Cassegrain focus) whilst Nyquist sampling the median summer seeing disc. When used in conjunction with the Nasmyth Adaptive Optics for Multi-Purpose Instrumentation (NAOMI) system and a second set of collimation optics, a high spatial resolution mode (0.04 arcsec pixel−1) is offered, providing near-diffraction-limited imaging. INGRID uses an all-refractive design and employs a cold stop to reduce thermal background emission, critical to the performance as it is used on the non-infrared optimized 4.2-m William Herschel Telescope (WHT). We discuss the design and operation of INGRID and illustrate its performance by discussing commissioning observations of the cluster Abell 2218 and the spiral galaxies NGC 3351 and 1530.